44 



TAGE SKOGSBERG 



Second method uj 

 explanation. 



Polycopidae, 



Sarsiellidac. 



Cypridinidae. 



Asleropidae. 



one- to four-jointed part of this limb seems to be homologous with the branch tiiat was 

 termed the exopodite in the preceding families. Cf. figs, IV: 7, 8. 



According to the second of the two methods of explanation mentioned above tlio fiftii 

 limb in the different families is in my opinion to be explained as follows: 



The vibratory plate corresponds to the exopodite. The greatest difficulty in carrying 

 out this homologization arises when we have to define the boundary between the protopoditc 

 and the endopodite. In this but rather little value can be attached to the position of the 

 vibratory plate; it is very far from improbable that this organ has been subject to not 

 inconsiderable alterations in position. The difficulty in fixing this boundary was really so 

 great that it seemed to me impossible to reach any definite result; there have always seemed 

 to be different possibilities present. 



Family Polycopidae: The protopodite either has the same extension as it has according 

 to the first method of explanation, i, e, it is more or less distinctly three-jointed, with a pro- 

 coxale, a coxale and a basale, or else it is formed only by the two joints on which the vibratory 

 plate is fixed. In the first case the nearest joint distaUy to the vibratory plate would correspond 

 to the basale and the outer of the two distal processes would correspond to the endopodite, 

 the inner being an accessor)^ appendage, an endite on the basale, cf. fig. VI; in the second 

 case the first-mentioned joint would correspond to the first endopodite joint and one of the 

 two distal processes is to be regarded as the end joint of the endoj^odite, the other as an 

 accessory appendage to the fii'st endopodite joint. In the former case the vibratory plate, 

 the exopodite, has been displaced proximally, but not in the second case. 



Family Sarsiellidae: As is seen above, this limb is almost entirely without any division 

 into joints. The large outer distal process is to be regarded as an endopodite, the small inner 

 distal lobe presumably as an endite either on the basale (cf. the accompanying figure VI) 

 or on the endopodite. 



Family Cypridinidae: The protopodite either has the same extension as according to 

 the first method of explanation or else it is represented only by the joint (or the two joints) 

 on which the vibratory plate is fixed. In the former case the joint nearest to the vibratory 

 plate distally is to be homologized with the basale, and the following joints correspond to the 

 endopodite; with this homologization the part that was denoted, according to the first method 

 of explanation, as the first and second exopodite joints would correspond to the first and second 

 joints of the endopodite; cf. the accompanying figure VI. In the latter case the joint situated 

 distally nearest to the vibratory plate is to be considered as the first endopodite joint; the 

 endopodite should have five joints in the accompanying figure. In the former case the exopodite 

 has been displaced proximally. 



Family Asteropidae: The comb seems to have been formed from the protopodite + the 

 two proximal endopodite joints or from the protopodite and the three proximal endopodite 

 joints. The long bristle (or the two long bristles) with tlie short bristles close to it 

 (or them) on the lateral side of the comb appears, according to this interpretation, to 

 belong to the two distal joints of the endopodite or to ow of these two joints; cf, the 

 accompanying figure VI. 



